Abstract
Endophytic bacterial population was isolated from Spartina maritima tissues, a heavy metal bioaccumulator cordgrass growing in the estuaries of Tinto, Odiel, and Piedras River (south west Spain), one of the most polluted areas in the world. Strains were identified and ability to tolerate salt and heavy metals along with plant growth promoting and enzymatic properties were analyzed. A high proportion of these bacteria were resistant toward one or several heavy metals and metalloids including As, Cu, and Zn, the most abundant in plant tissues and soil. These strains also exhibited multiple enzymatic properties as amylase, cellulase, chitinase, protease and lipase, as well as plant growth promoting properties, including nitrogen fixation, phosphates solubilization, and production of indole-3-acetic acid (IAA), siderophores and 1-aminocyclopropane-1-carboxylate (ACC) deaminase. The best performing strains (Micrococcus yunnanensis SMJ12, Vibrio sagamiensis SMJ18, and Salinicola peritrichatus SMJ30) were selected and tested as a consortium by inoculating S. maritima wild plantlets in greenhouse conditions along with wild polluted soil. After 30 days, bacterial inoculation improved plant photosynthetic traits and favored intrinsic water use efficiency. However, far from stimulating plant metal uptake, endophytic inoculation lessened metal accumulation in above and belowground tissues. These results suggest that inoculation of S. maritima with indigenous metal-resistant endophytes could mean a useful approach in order to accelerate both adaption and growth of this indigenous cordgrass in polluted estuaries in restorative operations, but may not be suitable for rhizoaccumulation purposes.
Highlights
Environmental pollution by heavy metals is a major concern for authorities (USEPA)1 due to several reasons: (i) its impact on environment and health, (ii) their high occurrence as a contaminant, (iii) their low solubility and bioavailability, and (iv) their carcinogenic and mutagenic nature (Davis et al, 2011)
The aims of this work were (i) to isolate the cultivable endophytes from S. maritima growing in salt marshes with different levels of metal contamination, (ii) to characterize them and select the endophytic plant growth promoting bacterial (PGPB) which might be useful for increasing plant biomass production, and (iii) to inoculate wild S. maritima seedlings in greenhouse conditions to elucidate the influence of these PGPBs in plant metal uptake in contaminated soils
In southwest coast of Spain, S. maritima is an endangered indigenous plant frequently used to restore degraded and contaminated salt marshes (Castillo and Figueroa, 2009). This species is included in European and National (Spanish) red lists which propose endangered species to be conserved (Cabezudo et al, 2005), since it is being displaced by the invasive S. densiflora (Castillo et al, 2008)
Summary
Environmental pollution by heavy metals is a major concern for authorities (USEPA) due to several reasons: (i) its impact on environment and health, (ii) their high occurrence as a contaminant, (iii) their low solubility and bioavailability, and (iv) their carcinogenic and mutagenic nature (Davis et al, 2011). The estuary of the Tinto and Odiel rivers, placed in the province of Huelva (Spain), is known as one of the most contaminated regions throughout the world due to the presence of high amounts of heavy metals in its sediments (especially As, Cu Pb, and Zn) since thousands of years (Nelson and Lamothe, 1993; Davis et al, 2000; Ruiz, 2001; Sáinz et al, 2002, 2004). This region has great environmental interest as well as historical significance (Wilson, 1981). 30 km away from this estuary, is located the Piedras estuary, with absence of relevant anthropic contributions and no significant metallic pollution which maintains its environmental quality (Borrego et al, 2013)
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